\documentclass[aspectratio=169]{ctexbeamer}
\usetheme[min]{sjtubeamer}
\begin{document}
\AtBeginSection[]{
  \begin{frame}
    \tableofcontents
    [currentsection, subsectionstyle=show/shaded/hide]
  \end{frame}
}
\include{maincontents.tex}
\end{document}